sel 0 cons X sel s cons sel X Z dbl1 s s1 s1 dbl1 X sel1 0 cons X sel1 s cons sel1 X Z quote s s1 quote X dbl 0 0 dbl s s dbls nil nil dbls cons cons indx nil nil indx cons cons from cons dbl1 0 01 quote 0 01 quote dbl X dbl1 X quote sel X Y sel1 X Y 2.2 NaTT certifiable-1.6